The present invention relates to an electrophotographic apparatus comprising an improved imaging system.
It has been proposed in the art to utilize focussing optical fiber arrays in the optical systems of electrophotographic apparatus such as electrostatic copying machines. The purpose of the optical system in such an apparatus is to focus an image of the original document onto a photoconductive member to produce an electrostatic image through localized photoconduction.
The focussing optical fibers are arranged in one or more parallel rows between the document and photoconductive member and relative movement is produced for scanning. Such an arrangement offers a number of advantages including reduction of the overall size of the apparatus, elimination of complex optical systems including mirror arrangements and evenness of illumination. In the latter case, to be more specific, the image does not vary from the center to the edges either in intensity or magnification. In addition, such an arrangement reduces image distortion, facilitates adjustment of image intensity and allows easy shielding of light from portions of the photoconductive member which are not to be exposed.
The image intensity has been controlled in the prior art by means of an adjustable exposure aperture provided between the optical fibers and the photoconductive member. Such adjustment is required for copying colored original documents so that the background prints white, copying low contrast documents and compensating for deterioration of the photoconductive member. In addition, adjustment is required to compensate for contamination of the optical system and other factors.
A serious problem has, however, been encountered in the practical embodiment of exposure control by means of an adjustable aperture in that a pattern of stripes is produced when the width of the aperture is excessively reduced. This is due to the fact that the optical fibers are arranged in rows which are spaced from each other.
Generally, an unevenness of intensity on the order of 2% is not noticeable, but unevenness on the order of 8% produces quite noticeable and objectionable striped patterns. An unevenness of 8% is often produced in practical applications involving copying certain types of documents.